Fuzzy retrieval is a retrieval method that allows fuzziness of data stored in a data base or fuzziness of retrieval conditions.
Fuzzy retrieval in the conventional fuzzy retrieval apparatus is executed in the following manner: A given retrieval condition is expressed by a membership function. From the data that has been stored in a data base, the data that corresponds to the retrieval condition is read out and the degree of membership with respect to the membership function representing the retrieval condition of the data that has been read out is calculated. Processing for calculating degree of membership is executed with regard to all retrieval conditions and with regard to all data corresponding to the retrieval conditions. The values of the degrees of membership thus obtained are subjected to a MEAN operation for obtaining the mean value of these values, a MIN operation for obtaining the minimum value of these values or a MAX operation for obtaining the maximum value of these values, and the result of the operation is outputted as degree of concurrence.
However, in a case where the MIN operation or MAX operation is used, a large discrepancy appears in the results of retrieval even with a small difference in the retrieval conditions or membership functions, and a problem that arises is that the user's intention in performing retrieval cannot be expressed accurately. In addition, when the MEAN operation is utilized, a problem encountered is that absolutely essential conditions or at least conditions that are required cannot be expressed accurately.
In other words, with the conventional fuzzy retrieval apparatus, it is difficult to set retrieval conditions in line with the user's intention in performing retrieval.